Exhaust produced by an engine may contain particulate, such as soot, creosol, and other hydrocarbons. Such particulate may be an artifact or byproduct of the combustion process. For example, soot may be an artifact of the combustion process (diffusion flame) in a diesel engine. As another example, engine generated particulate may be due to incomplete combustion brought on by engine operating conditions For example, at startup, an engine may run at a rich fuel to air ratio, producing incompletely combusted fuel in the engine's exhaust stream. Furthermore, changes in operating conditions, such as those brought on by increases or decreases in engine load, engine age, fuel quality and air quality may cause the generation of particulate.
Particulate filters, such as diesel particulate filters (DPF's) in diesel exhaust systems, may be used to filter exhaust leaving an engine. However, engine-generated particulate may collect on the particulate filters as the exhaust gas flows through porous walls, or flow-through walls. The collection of the particulate on the filter may lead to an increase in exhaust pressure, inhibiting filter functionality which may degrade engine performance. For example, increased exhaust pressure may decrease engine pressure by inhibiting engine scavenging and air intake. To clean or regenerate the filter, the particulate may be periodically combusted to reduce the collected particulate on the filter. However, when excessive amounts of particulate are present, the filter may suffer a significant temperature excursion due to heat transfer from the combustion of the particulate. This temperature excursion may result in permanent mechanical damage to the filter, including cracking and/or melting of the filter.
For example, U.S. Pat. No. 5,396,764 describes an approach for selectively filtering exhaust gases with a breathing bellows apparatus coupled to a particulate filter which may be used for storing and oxidizing exhaust. The bellows may respond to pressure changes brought about by increased temperatures, opening up one or more vents that allow exhaust to avoid the filtering apparatus. Another approach is described by U.S. Pat. No. 5,067,973 where a system of electronic feedback signals detect engine conditions, for example oxygen concentration, exhaust flow rate, etc., and control heating of a filter in order to combust particulate and achieve regeneration.
The inventors herein have recognized various issues related to these approaches. Heating to combust accumulated particulate and regenerate the filter may result in heat excursion which may permanently damage the filter and limit filter effectiveness. Furthermore, monitoring and controlling heating for regeneration with sensors may require complicated and expensive electrical and computational systems. Further still, even in filter devices where heating is controlled by added sensors and control systems, there may be a lack of available oxygen for combustion with particulate.
Accordingly, devices and methods are disclosed for reducing and/or preventing engine particulate filter failure. As one approach, a particulate filter regeneration system is provided. The system includes an exhaust inlet, an exhaust chamber coupled downstream of the exhaust inlet, an outlet, a flow-through wall coupled between the exhaust chamber and the outlet for filtering engine exhaust, a heater for regenerating the device, or engine based regeneration, and a bypass coupled to the exhaust chamber for opening a filter regeneration pathway. Operation of the particulate filter regeneration system may include accumulating particulate on the particulate filter, heating the device to enable combustion of accumulated particulate, selectively opening a bypass to enable exhaust flow through a filter regeneration pathway, and regenerating the filter.
By providing a filter regeneration pathway, more exhaust gases may be transported to and away from the exhaust chamber during regeneration to reduce and/or prevent the heat excursion on the filter. As such, the system enables the particulate to gas heat transfer to be maximized while reducing the particulate to filter heat transfer by reducing the amount of gas flowing through the filter walls during regeneration. Combusted particulate and other exhaust gases may be vented from the exhaust chamber as chamber exhaust. By transporting chamber exhaust away from the chamber, chamber exhaust may transport excess heat away from the filter through convection and act to cool the filter, inhibiting excursion.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.